Electrical musical instrument



ug- 30 1949- L. HAMMOND ET AL 2,480,132

ELECTRICAL MUSICAL INSTRUMENT Filed Jan. 16, 1946 5 Sheets-Sheet l Aug. 30, 1949. HAMMOND ET AL ELECTRICAL MUSICAL INSTRUMENT 5 Sheets-Sheet 2 Filed Jan. 16, 1946 Aug. 30, 1949.

L. HAMMOND ET AL ELECTRICAL MUSICAL INSTRUMENT Filed Jan. 16, 1946 5 sheets-sheet s ug. 30, 1949. l.. HAMMOND ET AL ELECTRICAL MUSICAL INSTRUMENT 5 Sheets-Sheet 4 Filed Jan. 1e, 194ee359 essa" Il IT T`T'TT C-Jas Augc 30, 1949 1 HAMMOND ET AL ELECTRICAL MUSICAL INSTRUMENT 5 Sheets-Sheet 5 Filed Jan. 16, 1946 POWER o- AMPLIFIER Patented ugl. 30, 1949 ELECTRICAL MUSICAL INSTRUMENT Laurens Hammond, Chicago, and John M. Hanert,

Park Ridge, Ill., assignors to Hammond Instrument Company, Chicago, Ill., a corporation of Delaware Application January 16, 1946, Serial No. 641,598 4s claims. (c1. sfr- 1.24)

The invention relates generally to electrical musical instruments and more particularly to an instrument of this character combined with a piano to produce accompaniment bass tones.

As more fully pointed out in the prior patent to John M. Hanert, No. 2,357,191, the musical scope of the piano is greatly enhanced by the addition of pedal clavier controlled electrical means to supplement the bass tone producing abilities of the piano. In accordance with the underlying principles of the present invention, the electrical bass tone producing means are in part controlled by the piano sustaining pedal so that the tonal output of the piano and of the electrical portion of the instrument are coordinated in rendering a musical selection. The pedal clavier electrical instrument thus is an integral part of the piano, not only physically, but with respect to the tonal output of the ensemble.

It is thus an object of the invention to provide an improved combined piano and electrical musical instrument in which the tonal output of the electrical portion of the instrument is controlled in part by the operation of the foot lcontrols of the piano.

A further object is to provide an improved musical instrument in which bass tones are produced under the control of the pedals of a clavier, and in which the duration of the tones are controlled in part by the sustaining or sostenuto pedal of the piano.

A further object is to provide an improved pedal clavier for the control of the output of an electrical musical instrument, in which there is provided a common means for controlling the tone intensity envelopes of all of the tones controlled by the pedal clavier. A

A further object is to provide an improved pedal clavier in which the operation of any one of the pedals causes the operation of a tone intensity.

envelope controlling instrumentality in response to the velocity of depression of the pedals of the clavier.

A further object is to provide an improved pedal clavier for electrical musical instruments having electrical circuits controlled thereby which are effective to cause the tone of the last depressed pedal to persist with gradual decay until a second pedal is depressed.

A further object is to provide an improved electrical musical instrument having a pedal clavier and an oscillating tone signal generator tuned to the note frequencies of the various pedals upon depression of the pedals, and in which the generator is maintained in operation at the frequency corresponding to the last depressed pedal until another pedal is depressed.

A further object is to provide an improved pedal clavier having a plurality of switches, at least one operated by each of the pedals, and in which each operated switch is maintained in operated condition and released only upon the depression of another pedal.

A further object is to provide an improved electrical musical instrument in which the tone and its octave are simultaneously produced, and in which the higher tone decays at a more rapid rate than the lower tone.

A further object is to provide a variable quality tonal decay envelope in which two tone generating sources, generating signals of different amplitude and in phase relation are employed, and in which the decay rate of the lower amplitude signal is faster than the decay rate of the higher amplitude signal, whereby the quality of the composite tone will change as the tone decays.

A further object is to provide a touch responsive control tube system in `which the exact characteristics of the control tubes are relatively unimportant.

A further object is to provide a touch response control tube mechanism and circuit in which the decayof the note is substantially asymptotic to zero amplitude.

A further object is to provide a touch responsive control tube system in which spurious effects of interelectrode lcapacitance and grid rectification are obviated by removing the input signal as well as the DC plate supply source from the control tube.

A further object is to provide a tone quality generating mechanism in which tWo primary so-urces of fundamental frequency signals are provided in 180" phase relation and in which amplitude limiting means are provided to convert the signals .into symmetrical rectangular pulses, and in which further rectification means are provided to convert the symmetrical rectangular pulses into assymetrical tone signals thereby to produce a long and desirable series oi both even and odd harmonics.

A further object is to provide a musical instrument in which the quality of the tone changes smoothly over the compass of the instrument, the lower pitch tones being progressively richer in harmonic content.

A further object is to provide an improved electrical musical instrument having a plurality of keys, in which each key is provided with a plurality o f switches operated in a predetermined order to provide an intensity envelope controlling circuit responsive to the time interval between the operation of several of the key operated switches, and in which relay means controlled by one of the key operated switches are provided to control the transmission to the output of the instrument of the selected tone signals.

A further object is to provide an improved electrical musical instrument having a keyboard, a tone signal generating system, and a plurality `o'f switches operated by each of the :keys :of vthe keyboard, one of the switches of each key being provided to close a circuit through one winding of a relay, in which a subsequently operated key switch controls the pitch of the 'tone produced by the instrument.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Figure 1 is a perspective View illustrating the manner in which the electrical iportion of the instrument is combined with the mechanical or piano portion thereof:

Figure 2 is a plan view'of the pedal clavier with a portion of the top of the casing removed to show 'the operating parts;

Figure 3 is a vertical sectional view taken on the line 3-3 of Fig. 2;

Figure 4 is a fragmentary vertical sectional view taken on the line 4-4 of Fig. 2;

Figure 5 is a schematic wiring diagram of one form of the invention;

Figure 6 is a schematic wiring diagram -of a modified form of the invention;

Figure '7 is a diagrammatic view of a key vand the switch operating means employed in the instrument shown in Fig. 6; and

Figure 8 is a schematic wiring diag-ram of a second modified form of the invention.

Referring to Fig. l the instrument comprises a piano of conventional construction, a pedal vclavier 2, a speaker and electronic component containing cabinet 3 connected to the pedal clavier lby a multi-conductor cable 4 and ya `box 5 connected to the pedal clavier by a cable v-6 and 'containing one or more switches oper-able by the `sustaining pedal or the sostenuto pedal ofthe piano. The pedal clavier includes ahousing comprisinga base Ill (Figs. 2 and '3) and a cover I2. The base I0 is preferably provided with pads l`4 and vlli of rubber or similar'material, the pad I6 providing a rest surface for `the vheel vof the player. The pedal clavier illustrated includes seven natural pedals I8 and five sharp pedals 20, the instrument thus having a gamut of one octave. The natural pedals I8 each-comprise a channel shaped key bar 22 pivoted on `a half round ulcrum rod 24, the key bar 22 having 'suitable arcuate Arecesses 25 complementary to vthe Vrounded surface of the fulcrum rod 24. In a .Ward motion of the forward ends of the key bars 22. In a similar manner the key bars 26 for the sharp pedals 2t are held against lateral displacement by `a comb 32 which VValso forms the ldown 4 stop for these pedals. The combs 30 and 32 are preferably covered with felt on all surfaces which may contact the key bars.

Due to the spacing of the fulcrums 24, 28 the rearward ends of the key bars 22 and 26 will have the same extent of upward motion upon depression `of their lpedals. The downward movement of the rearward ends ofthe key 'bars 22 and 26 is limited by their engagement with a felt pad 34 which thus forms the up stop for the .pedals I8 and 20.

Each of the key bars 22, 26 is provided with a felt pad 36 which is engageable with a tubular cross bar 38 of a bail which also includes three bail arms 40, 4l and 42. The forward ends of these bail arms are pivoted to a rod 46 which is supported from the base lll by a pair of bearing brackets 48, 49. Upward movement of the bail arms 4'0 and 4l is limited by a stop bracket 5U, provided with a felt pad 52. The bail is normally -held in its down position, in which it is shown, by a tension spring 54, one end of which is hooked over an ear 56 forming part of bail arm 4I and the 'other end of which is anchored to a clip 58 secured to an insulating cross bar 60. Each of :the pedal bars 22 is resiliently biased to the positions 'in which they are shown in Fig. 3 by a suitable spring !52 while the sharp key bars 26 are biased to their normal Ipositions by suitably mounted springs 64.

'The center bail arm 4| has a spring pressed pawl 66 pivoted thereto, the tooth portion of the pawl normally resting in a notch 68 formed in a throw out element it which is rigidly secured to a rotatably mounted shaft 12, the element 10 having a tail portion 14. Rigidly secured to the `shaft 12 is an yarm 13 and insulating pads 16, each Yhaving a latching spring finger 18 normally lying adjacent the upper or rearward surface thereof. These spring fingers 'i8 normally engage `the-ends of Switch arms'Sll, as shown in Fig. 3, but lare .adapted to flex forwardly (to the right, Fig. '3) Whenever the adjacent switch arm 8l] is raised, and thus assume a latching position beneath the switch arm to hold the latter in raised position. The switch arms 80, of which there is one for each pedal, except the lower C pedal, are secured to the insulating cross piece 60, and normally press against the upwardly extending end portion of a relatively rigid complementary switch arm 82. Each of the key bars 22, 26 is provided with a suitably insulated actuating pin B4 which may be rigidly secured vto the key bar and the upper end of which is adapted to engage its associated resilient switch arm 80 and raise the latter from contact with the end of the relatively rigid switch arm 82 to open the switch.

Since the bail rod 38 overlies the ends of all of the key bars 22, 26 the bail is swung clockwise "upon depression of any one of the keys. During the -upward movement of the bail, the point of lthe pawl '66 engages in the notch 68 and swings the element 10 counter-clockwise so that the arm 13 which is secured vto the shaft 1.2 is raised from ,its-stop pad v'l5 and moved against the tension of the suitably anchored spring 11. As thebail continues moving upwardly the tail portion 14 of the throw-out element 1|) engages the pawl 66 and pushes it out of the notch 66, whereupon the Yspr-ing 11 vwill swing the rarm 13, shaft 12, and 'element 'lil clockwise until arrested by the stop .pad 15. It will be clear that this release of the pawl "66V from the element 10 will occur prior to `the completion of the up stroke of the pawl.

T5 Thus 'the push rod of the particular pedal 'which has been depressed will hold its associated resilient switch arm 80 upwardly in a position above the end of the spring finger 18 so that upon subsequent release of the depressed pedal the switch arm 80 will be held by the spring iinger 18 in a position so as not to make contact with the switch arm 82. As a result, the switch 80, 82 of the last-depressed pedal will remain open until another pedal is depressed. 'I'he purpose of this will appear more clearly from the description of the electrical circuits controlled by these switches.

A pair of wiping commutator type switches 90 and 9| (shown diagrammatically in the lower left hand corner of Fig. 5 and shown in elevation in Fig. 4) are operated by the bail 4|. The switch 90 comprises a lever 92 suitably pivoted on a stud 94 and having an elongated slot 95 engaging a pin 96 suitably secured in the end of the tubular bail rod 38. The moving element of the switch 9| comprises an arm 98 which is secured are suitably mounted on an insulating plate ||4 carried by a bracket I6, the latter being secured to the base I0. The contactors |00 and |0| may be resiliently mounted on the lever 82 and arm 96, respectively, or the latter elements may be resiliently biased to maintain these contactors .Y

in good electrical contact with the segmental contacts.

From the foregoing it will be apparent that as any one of the pedals is depressed the contactor |00 will successively make contact with the segmental contacts I 02|06 and similarly the contactor |0| will make contact with the segmental contacts |08- I |2, and that the length of time that these contactors are respectively in contact with the segmental contacts |04 and ||0 will depend upon the velocity with which the pedal is depressed.

As the lever 92 and arm 96 approach the positions in which their contactors reach the segmental contacts 06 and ||2 respectively a projection ||8 on the lever 92, having an insulating actuator |20 secured thereto, opens switches |22 and |23. This occurs prior to the time that the contactors |00 and |0| make contact with the segments |06 and 2 respectively.

Referring to Fig. 5, .the electrical portion of the instrument comprises a push-pull oscillator consisting of a pair of pentodes |30, |3|. A voltage of fixed potential is impressed upon the screen grids |38, |31 of these pentodes through a. voltage dropping resistor R|38 which is connected to a suitable source of plate current potential indicated as a terminal +300 V. By pass capacitor C|40 connects the screens |36 and |31 to ground. Plate voltage is supplied to the plates |42, |43 of the pentodes |30, |3| through plate load resistors R|44 and R|45 respectively. The cathodes |46 and |41 are connected to ground through a common biasing resistor R|48. A tuning inductance L|50 has a grounded center tap and has its terminals connected respectively to the control grids |52 and |53 of the pentodes |30 andY |3|. Feedback paths from plate |42 to grid |53 and from plate |43 to grid |52 are provided through resistorsl R|55 and R|56 respectlvely. The terminals of the inductance L|50 are also connected respectively to conductors |60 and |6| across which one or more of twelve tuning capacitors C|62 may be connected. Each of the pedals, upon depression, opens a switch 80, 82 associated therewith, `these switches being connected in series so that the highest of several depressed pedals renders inelective the depression of the lower pedals. The pedal for the note C is not provided with a switch 80, 82, since the oscillator will be .tuned to the frequency of the lower C when all of the switches 80, 82 are closed, due to the fact that under these circumstances all twelve capacitors are effectively connected in parallel with the inductance L|50.

The pentodes |30 and |3| operate as oscillators at the same frequency but in 180 phase relation. Due to the push-pull connection of pentodes |30, |3|, the plate voltage will have a symmetrical wave form consisting substantially of the fundamental and the odd harmonics thereof; the even harmonics will have been cancelled. This wave shape is illustrated in Fig. 5 by the curve |10 which is located above the circuit in which it appears.

The output of the pentodes I3, |3| is coupled to the input circuits of triodes |12, |13 through blocking capacitors C|14 and series grid resistors R|16, grid return paths being provided by grid resistors R|18 which are connected to ground. The cathodes of triodes |12, |13 are likewise connected to ground while their plates are connected to a suitable source of plate potential +300 V., through load resistors R| respectively. Due to the grid rectiiication and the current limiting action of the series grid resistors RHS, a rectangular wave is generated at the plates of the tubes |12, |13, as indicated by the curve |82 appearing above one of the circuits in which this wave appears. It will be understood that the output of the triode |13 will have a wave similar to the curve |82, but of opposite phase.

The output of the triodes |12, |13 is coupled to the input oi triodes |84, through small current limiting capacitors C|86 and C|81 respectively. The grids of the triodes |84, |85 are connected to a negative bias source illustrated as a terminal -35 V. through a series grid resistor R|88 and grid return resistors R|90. The cathodes of these triodes |84 and |85 are connected to ground. Due to the fact that triodes |84 and |85 are provided with a negative bias voltage (-35 V.), the Waverepresented by the curve |92 which appears between the capacitor C|86 and resistor R|88 has only the positive peaks thereof effective 4to produce plate current ilow in these triodes. As a result, the plate voltage wave appearing on the plates of triodes |84 and |85 will be in the form of a series of positive peaks corresponding to the peaks of the wave as indicated by the curve |94. Plate current is supplied Ito triodes |84, |85 through plate load resistors R|96 and R|91 which are connected to conductors |98 and |99 respectively. As will be described hereinafter, the amplitude of a signal, such as represented by the curve |94, is generally directly proportional to the voltage appearing on the conductor |98 while the corresponding Wave appearing at the plate of the triode |85 will be of amplitude generally proportional to the average potential on conductor |99. The two waves from vthe outputs of the triodes 84, |85 will be of phase relationship.

The outputs of the triodes |84, |85 are coupled to the inputs of triodes 200 and 20| through blocking capacitors C202 .and C204 respectively and series grid resistors R204 andR205 respectively. The grids Vare connected to .ground through the series grid Yresi`storsrR204, R205 and grid lreturn resistors R20|,:R2|l'|, The vcathodes oflth'etriodes 200 and 20| fare connecteddirectly to ground. Plate voltage is supplied .tothe `plate of triodes 200, through a lloadresistor R208 connected to the conductor |98, while'plate voltage is supplied to the triode .20| through load resistor R209. The triodes 200 and.'20| function 'as amplitudelimiterstochange the form of fthe signal from that shownby the'curve |94 to that ofthe curve 209.

The signal 'voltage appearing .atfthe plates of y the triodes 200 and 20| will, as more clearlyappear hereinafter, .he substantially "proportional tothe voltageappearing on the conductors |98 and l99'respectively. It will alsobe clear rthat When'the voltage on conductors l98and |99 is zero, the signalen `thegrids of triodes 200 'and 20| lwill 'beY substantially Zero. It rwill -therefre be apparent that the :signals at the 'plates Vof the triodes Ze and `20| 'will vbe zero.

The output of the triode 200 is-coupl'edthrough 'a decoupling resistor R210 toa signal 'conductor 2|2 While the output of the triode20`| is similarly connected to the conductor 2|2 through-.a resistor R2I`I. The conductor 2|2 is connected to ground through a capacitor C2 |13 Which..provides a Vbyepass for undesirably high harmonic `frequencies. The resistor R210 is .preferably of a value approximately 'one half that of'7R2l l, with the result that the signal appearing on conductor 2|`2 will be of the wave shape illustrated bythe g5 curve 2|0. It will be noted that this curveirepresents a predominantlyV even harmonic 'series which corresponds to a strong octave harmonic component, for instance, similar tothe effect of striking the octave on the piano. generally rectangular voltage excursions appearing on the wave 2id' are due to thesignal-from the t'riode 200 While the lower voltage excursions are due to the signal from the triode 20| provided by the decoupling 'resistor vR2| l. .The idimension t of the wave'2l6isrelatively constant irrespecti've'of the frequency at Which-'the 'oscillator 13e, |3| operates, but as the oscillation frequency decreases the proportion of ti relative to the duration ofthe cycle, (the Ydimension 'I 50 ofthe curve 2|9) becomes less. As this .occurs .the harmonic content of the Atone 'represented by this signal increases, thus, it becomes brighten This is a desirable feature :since low pitch tones having vhigh .harmonic developuponthe voltage appeaiingupon conductor |98.

On the other hand, theinte'rmediate low .amplivtu'de peaks of the'wave 'le arederived from the signalappearing on the platec'f triodefzl :and

Y thus depend upon the voltage .appearinglup'on conductor |99.

The voltages appearing` on the -conductors l |98 'and |99 are respectively .controlled bythe commatter.

The Nhighest l mutatingfswitch mechanisms 90 and 9| previously described. In these switch mechanisms the comfmutator segments |02 and |08 are connected toa 'suitable highpotential source indicated as a terminal -l-300 V. through small anti-spark resistors The contactor |00 is connected toground through a capacitor C222 which has a discharge resistor R224 in parallel therewith. In a similar mannerthercontactor I0| is connected to ground through a capacitor C223 having aresistor R225 in parallel therewith. The Valueslof the capacitor C222 with respect to its parallel resistor R224 is such-that the drop in Voltage due t0 leakage of the charge of the capacitoracross the resistor R220 will be at a rate such that thesignal appearing on .the plate of the triode 200 will decay in substantiallyV the s-ame manner vas a sustained bass tone of a well constructed piano. Assuming capacitors C222 and C223 to .be of the same value, the resistor R225 would be of a value of approximately one half of that of the resistor R224. Thusthedischarge'rate of the capacitor C223 wouldbe twice that of the capacitor C222. The significance of these-differing discharge rates will appear here- The segments |03, |05, |09 and do not have any electrical-connections thereto. The segment It is connected through discharge resistors R230 and R232 to a suitable sourceof constant low voltage (e. g. 9 volts) shown as va terminal indicated :as +9 V. In a similar manner the-segment |10 is connected to the +9 V. terminal through discharge resistors R23| and R233. To change the rate of discharge, the resistors R232 and R233 may be shunted out of their circuits by closure of switches 236.

The segment |06 is connected to conductor-|99 through an -attack'resistorR238 while the *segment ||2 Vis `similarly connected to the conductor |90^through an attack resistor R239. The con-- ductors |98 and |99 are connected Vto ground Ythrough potential storing capacitors C240 and C24| respectively. Disregarding for the moment the remaining connections to the segments |00 and H2, it will appear that the capacitors C222 and C223 are each initially charged to a potential of +300 Volts. As the contactors |00, 10| 'swing clockwise along the commutator segments and engage the Vcenter segments |05 and ||0, vthe potential on the capacitors C222 and C223-decreases rapidly `due to the discharge of these capacitors throughfresistors R230--R232 and vR23|R233 respectively. Thus when the con- .and-024| will likewise be charged topotentials depending upon the velocity at which the pedal is depressed. Therefore, the amplitude of the signal appearing upon the'conductor 2|2 will be determined by the velocity of` pedal depression.

Before the -contactors |00, |0| leave segments |04, i H0 respectively they open switches|-22 'and |23. Upon removing the foot from the pedal,

"and upon the consequent vreturn swinging `movement ofthe bail .rod 38, the contactors |00, |0|

Afwill-.swing counterclockwise, and afterlcont-actlng the segments |04, H0, will permit switches Y.|22

4and"|23 to'close. These switches are connected t0 the :segments |06 and ||2`through resistors.

R246 and R241 respectively. The switches |22 and |23 are connected in series respectively with switches 250, 25 I, the other poles of these switches being connected to ground. The switches 250 and 25| are adapted to be operated Whenever the piano sustaining pedal 252 or the sostenuto pedal 254 is depressed. Thus when the contactors and |0|, on the return stroke of the bail, leave the segments |06, I2, and close switches |22, |23, the charge on the capacitors C240 and C24| is dissipated relatively rapidly through the resistors R238 and R239, R246 and R241, switches |22, |23 and switches 250, 25| to ground, because the values of the resistors R238, R230, R240, R246 and R241 are low relative to the plate load resistors R|96, R191, R208, R209 and the internal plate resistance of the triodes 200, 20| as Well as the internal plate resistances of the triodes |84, |85. However, if either the sustaining or damper pedal 252, or the sustenuto pedal 254 is depressed, such discharge of the capacitors C240, C24| can not take place and the only path for the discharge of these capacitors is through the plate circuits of the triodes 200 and 20| as well as the plate circuits of triodes |84, |85. The time constant of the capacitor C222 discharging through the resistor R224 is made substantially the same as the time constant of the lcapacitor C240 discharging through the plate circuits of the triodes |84 and 200. Similarly the time constant of the capacitor C223 discharging through the resistor R225 is made to be substantially equal to that of the capacitor C24| discharging through the plate circuits of triodes |85 and 20|.

The output signals of the triodes 200 and 20| appearing on the conductor 2|2 are coupled to the input of a phase splitting triode 260 through a blocking capacitor C262 and a volume control resistor R264 and a second blocking capacitor C266. The cathode of triode 260 is connected to ground through self-bias resistor R268 and a load resistor R210, the junction of these resistors being connected to the grid through a grid resistor R212 and being connected through a blocking capacitor C214 to the grid of a triode 216. The plate of triode 260 is connected through a capacitor C218 to the grid of a triode 280. Operating plate voltage for the triode 260 is supplied from a suitable source, indicated as +300 v., through a load resistor R282. The grids of triodes 216 and 280 are connected together through a capacitor C284 which by-passes undesirably high harmonic frequencies present in the signal. The cathodes of triodes 216 and 280 are connected to ground through a biasing resistor R286 while the grids thereof are connected to ground through suitable grid resistors R288. The plates of the triodes 216 and 218 are connected to the terminals of the primary winding of a driver transformer T2 90, the center tap of which is connected to a suitable plate current source, +300 V. A capacitor C292 connected across the terminals of the primary of T290 oifers a further path for ley-passing undesirably high harmonics of the signal. The secondary of transformer T290 has its terminals connected to the grids of class B power amplifier triodes 294' and 295. A capacitor C295 is connected between the plates of triodes 294 and 295 offering an additional by-pass path for undesirably high frequency harmonics. A power output transformer T298 has the terminals of its primary connected to the plates of triodes 294, 295 and has its secondary winding connected in parallel to the voice coils of speakers 3,00, 30|.

In view of the fact that the triodes |84 and |85, and 200 and 20| operate in a non-linear manner, it is unnecessary that their characteristics be maintained with a high degree of precision as might be necessary if they operated as class A amplifiers. In their operation they are either operating in one of two conditions, namely, full plate current or completely cut off plate current. By virtue of this fact a large series of extremely high harmonics are introduced into the signal by the distortion and it is therefore necessary to repeatedly filter the signal as by means of the bypass capacitors C2 I 4, C284, C292 and C296. These capacitors round oil' the corners of the signal wave shape and make the resulting tone more pleasing to the ear.

In view of the fact that the time constants of the capacitors associated with the commutating switches and 9| are different, the signal appearing on the conductor 2|2 will initially be of the form indicated by the curve 2|6. Since the plate potential on the triode 20| drops more rapidly than that of the triode 200, the smaller intermediate peaks wll decrease in amplitude much more rapidly than the higher amplitude peaks of the wave. In fact, the smaller amplitude peaks will decay to such low value as to be inaudible in the ultimate tone produced while the higher amplitude peaks of this wave will still provide a clearly audible signal. This is of distinct musical advantage because at lower volume levels the ear is less sensitive to low frequencies and therefore the removal of the high frequencies tends to produce a bass compensation effect which is highly desirable from the musical standpoint. Also the tone is more interesting in that its quality continuously changes as the tone decays.

Since the intensity of the tones produced by the instrument may readily be controlled by the player in response to the velocity at which he depresses the pedals, it is unnecessary to provide additional volume controls. The variable resistance volume control provided by resistor R264 is preferably an adjustment which is made upon installation of the instrument in a particular location, and is designed to provide sufcient bass radiation to be acoustically equipped for the particular room or auditorium in which the instrument is to be played.

Under some circumstances it may be desirable to alter the degree of pedal velocity responsiveness of the instrument. This may readily be accomplished by closing the switches 236, thereby shunting resistors R232 and R233 from the capacitor discharge circuits. Under these circumstances, the rate of discharge of the capacitors C222 and C233 to the +9 V. terminal will be controlled mainly by the resistors R230 and R23I respectively. When these switches are closed, the sensitivity of the velocity of pedal depression is substantially increased, and the effect corresponds in sensitivity to that of the piano keys. The absolute values of the resistors associated with the attack and decay control circuits must not only be correlated with the values of the capacitors employed in these circuits, but must also be correlated with the physical dimensions and the inertia of the pedals, and to the spring tension applied thereto. In other words the speed with which a pedal may be depressed by an average player will determine the constants of the electrical components of the attack and decay circuits, particularly the values of the capacitor discharge resistors R230 and R23I.

In the use of the instrument it is placed in a position relative to the piano as shown in Fig. 1 with the switches 250, 25| arranged to be opened upon depression of either of the damper or sustaining pedal 252, or the depression of the sostenuto pedal 254 of` the piano. In playing the instrument the musicianY need merely tap the pedals,V I8, V20 with the desired velocity requisite to produce tones of the desired loudness. The tone will continue to soundv for an interval after thel release of the pedal, since theswitch 80, 82 associated with the depressed pedal will be retained in open position bythe spring ringer 18 after the pedal is released. VIt will be recalled that the switch 80, SZIdetermines the frequency of operation of the oscillator |30, |3| and the oscillator will thus maintain the frequency to which it was adjusted by opening of the particular switch 80, 82 until the charges on the capacitors C240 and C24| have been dissipated Vthrough the plate circuits of the triodes |84', |85, 200 and 20|. Ii prior to the nal decay of a tone to an inaudible intensity a second pedal is depressed, depression of the latter will, due to the action of the pawl 66, move the spring linger 18 associated with the previously depressed pedal from beneath the switch arm 80 and permitthe latter to close, while at the same time, the push rod 84 of the second depressed pedal will raiseits switch arm B above the end of its associated switch nger 18 so that this switch 80, 82 will thereafter remain open. The amplitude of the second tone will in all probability bek increased over that of the remaining portion of the first tone due to the increase in charge on the capacitors 2aB, 24| during the operation of the commutating switch mechanisms 90, 9|. It is possible that the volume could also be reduced by the subsequent depression of a second pedal but this is rather unlikely.

The technique of playing the instrument is greatly simplified due to the provision of the mechanism and circuits by which a note continues to soundl after the pedal controlling it is released. This gives the musician adequate time to shift from one pedal to another without silence between successive pedal notes. It also enables the player to play the pedalboard in a more leisurely manner so that ample time is always afforded between the initiation of the successive tones, which latter time is substantially wholly utilizable by theV player in moving hisfoot from one pedal toV another. This feature is of great importance and constitutes a substantial improvement over other pedal operated instruments such as the organ, in which the player must of necessity retain his foot upon the pedal throughout the time interval that he desires the note to sound and, as a consequence, little time is allowed for shifting his ,foot from one pedal to another. Thishas constituted alserious limitation on the rapidity with which pedal passages could be played'upon the pedalV claviers of prior instruments, using but one foot.

If desired, substantially the same results attained by the instrument as shown in Figs. 1 to 5 with the opening of switch 35|. Thereafter, following a suitable time interval depending upon the velocity with which the pedal 350Y was depressed, the switches 352 and 355 are opened and the switch 35S closed.

The` switches 35| are connected in serieswith a source of operating potential shown as a terminal +300 V. through a small anti-spark resistor R355. The switches 352 are likewise connected in series and are connected to a +9 V. terminal through discharge resistors R358 and R359. The resistor R355 may be shunted upon ciosure of a switch 355 when it is desired to increase the discharge rate. lit will be clear that the switches 35| and 352 associated with the pedal B are connectedthrough a conductor 352 and a relay transier switch 351i to a capacitor C350, the other terminal-of this capacitor beingconnected to ground. The transfer switch 55E; operated by a relay winding 353 which is energized upon closure of any one of the switches 353 since it will be noted that one pole of each of these switches is connected to a +5@ V. terminal while the other pole oi each or" these switches is connectedv directly to the'ungrounde'd terminal of relay winding 350. When the relay 358 is energized the transfer switch arm 355 connects the capacit-or C355 to conductor El@ through an attack resistor R312. Energization ci the relay also opens switch 3M, prelerabiy before the switch arm 364 connects the capacitor 355 to the resistor R312. The switch 314 is in a circuit connecting the conductor 3'50, a resistor R375, a piano damper pedal operated switch 373 and ground. rJhe conductor 310 is connected to ground through a capacitor C380, which corresponds in function to the capacitors C2G@ and C'Z't! of Fig. 5.

It will be' recalled that the switch 355 is closed during the early part of the downward movement of a depressed pedal 355. Each of these switches is adapted to complete a circuit from a suitable source, indicated as +50 V., through one winding of a double winding relay BSZ, to ground. When a relay 332 is thus energized it closes its switch 383 tending to temporarily complete a holding circuit through the other winding on the relay. This holding circuit includes the +50 V. source and the series of switches 354. The latter switches are subsequently opened upon further depression of the pedal but the relay 332' is maintained energized because the associated switch 355 is still closed. Upon release of the pedal the switch 55d closes and thus recompletes the holding circuit initially completed by the operated relay switch 383.

in addition to operating the switch 383, each of the relays upon energization open a tuning switch 384. These tuning switches are connected in series to a conductor 535 and each also has its stationary contact connected to one terminal of a tuning capacitor C388, the other terminals of these capacitors being connected to a conductor 390. The twelve tuning capacitors 383 are thus in parallel with a tuning inductance L392 when Vall of the switches 38d are closed. When any one of the switches 33d is opened upon energization of its associated relay 382, the capacitors C580 associated with pedals of lower pitch are disconnected from the tuning circuit. It will thus appear that the oscillator which includes the inductance LBS?! will remain tuned to the frequency determined by a depressed pedal even after the pedal is released, in the same manner as in the previously described embodiment. Upon initial depression of a second pedal the associated relay 382 will be energized in the same manner as previously describedbut upon further depression of the second pedal, its associated switch 354 will open the common portion of the holding'circuits for all of the relays 382 and thus the holding circuit for the previously energized relay 332 which was held energized by its holding circuit, will be deenergized and only the relay associated with the second depressed pedal will remain energized.

The push pull oscillator and Wave shape amplifying and amplitude controlling tubes operate in the same manner as those in the previously described embodiment and similar reference characters have therefore been applied to corresponding parts. It will be noted, however, that the intensity envelope controlling circuits for the form of the invention shown in Fig. 6 differ from those shown in the embodiment of Figs. l to in that the conductor 3l@ which supplies the controlling potential to the plates of the triodes |84, |85, 230, 20| is connected to the plates of all. of these tubes through their associated plate load resistors.

Instead of having the cathodes ofl both triodes 20!) and 29| connected to ground, the cathode of triode 23|! is connected to a constant potential source (indicated as '+I V.) slightly above ground potential, while the cathode of triode 29| is connected to a source of constant potential such as a +9 V. terminal. As a result, the signal controlled by the triode 20| will decay to inaudibility prior to the decay to inaudibility of the signal transmitted by triode 2&0. Since the cathodes of both triodes 20|) and 28| will be at a positive potential with respect to their plates when the capacitor C383 is fully discharged, the triodes 234 and 2i!! will be incapable of transmitting any signal. A further reason that the triode Zilli will be completely cut off is that there is one volt negative bias on its grid. Thus as the tone decays, the octave producing component thereof will decay to inaudibility while the fundamental producing component is stillquite audible. The remaining portions of the output system of the instrument may be similar to that previously described with reference to Figs. 1 to 5.

In the embodiment of the invention shown in Fig. 8 the oscillator is tuned, as in the previously describedV embodiments by the operation of pedal actuated switches 32 which determine the number of capacitors Cibi? connected in parallel with the tuning inductance 1.453. The oscillator of Fig. 8 comprises a pair of triodes 49!! and 44| having their grids respectively connected to the terminals of the inductance LIS!) and having their caihodes connected to the grounded center tap of inductance L|55 through a self-biasing resistor R432. The plates of triodes 400 and 40| are connected to a suitable operating potential source, indicated as +3552 V., through load resistors R404 and R435. The terminal of the inductance 1.453 which is connected to the grid of triode 469 is connected to the plate of triode 40| through a resistor R485 and a blocking capacitor C439 ..vhile the terminal of L|5ll which is connected to the triode 43| is connected to the plate of triode 405B through a resistor R401 and blocking capacitor C408, these circuits providing the regenerative feedback necessary to secure self-oscillation.

The outputs of the triodes 400, 48| are coupled to the grids of triodes 4|!) andv 4|| through grid resistors R4| 2 and R4|3. The grids of triodes 4|0 and 4| l are connected to ground through ca- 'l in pacitors C4|4 and C4|5 respectively. These capacitors function to suitably round off the peaks of the signal waves as supplied by the oscillator. The cathodes of the triodes 4| and 4l are connected to a suitable source of negative potential .indicated as a terminal -50 V. through selfbias resistors RMS and R4H respectively and are connected to ground through bias-storing oapacitors C4|8 and C4|9 respectively.

The self-biasing resistors Rl are of substantial value such as 5 meg-ohms each so that the grids oi the triodes MS and 4|| will be highly biased in a negative direction and consequently only the highest positive peak signals Will be effective to causo pulsations of plate current to flow, in a manner similar to that more fully disclosed in the patent to Gilbert Smiley, Reissue No. 20,831. Plate current is supplied to these triodes from source indicated as +3ll V. through load resistors R423 andn R42| respectively. The plate of triode 4H) is connected to an output terminal 422 through a decoupling resistor R424 while the plate of triode 4|! is con-- neoted to said terminal 422 through a decoupling resistor R425. The plate of triode C4|Ll is connected to ground through a capacitor C423.

The value of R424 is preferably made equal to R425, and. R42ll is likewise preferably made equal to R42l. If the capacitor C423 were not connected in the circuit, asignal at the junction point 422 would be of double fundamental frequency and would thus sound at the interval of the octave. The capacitance C423 is chosen of such value as to limit the output amplitude of triode 4| to approximately one half that of triode 4H at the low end of the pedalboard compass (32.7023 C. P. SJ, and thus produces a composite tone of the octave in which the octave harmonic series .is of a somewhat more mellow tone quality than the fundamentall harmonic series. Thus as the musician plays up the scale the effect is one of a smooth reduction in the degree of octave tonality, the latter effect being very desirable from a practical standpoint. This is because the impedance of the capacitative reactance of C423 is considerably greater relative to the other constant-r resistive impedances of R420, R42|, R424 and R425 at the high frequency end of the pedalboard. Thus the octave coupler effect is large at the bass end of the pedalboard, and small at the treble end.

The output of the triodes 4||J and 4|| is impressed upon the grid or a preamplier triode 428 through a blocking capacitor C429. The triode 428 operates as a phase-inverter to change the single-end output which appears at the terminal 422 into a push-pull output, and its cathode is therefore connected to ground through a biasing resistor R430 and a load resistor R43I, the junction 432 between these resistors being connected to the grid of the triode through a grid resistor R434. The plate of the triode 428 is connected to a. suitable source of operating potential such as 3|!!! V. through a load resistor R435. The signals of opposite phase respectively appearing at the terminal 432 and at the plate of the triode 428 are transmitted through blocking capacitors C438 and C439 respectively to the control grids of pentodes 44| and 440. The pentodes 44S and 44| are preferably of the variable mu or remote cut-off type. Their variable gain property is utilized to obtain Various noteintensity envelopes substantially free of distortion.

The control grids of the pentodes 440 and 44| are connected to a suitable negative biasing pol tential source, such as the terminal -60 V., through grid resistors R442 and R443 respectively and through a common relatively high value resistor R444, the value of the latter being preferably in the order of 5 megohms. The cathodes of pentodes 440 and 44| as well as their suppressor grids are connected to ground, while the screen grids thereof are connected through a voltage Ydropping resistor'R446 to a suitable potential source such as a +300 V. terminal. The screen ygrids are also connected to ground through a zero volume adjustment resistor R448 which, together with the resistor R445, forms an adjustable voltage divider to determine the potential on the screen grids of these pentodes. The plates of these pentodes are connected to the +300 V. terminal through load resistors R448 and R449 and the output of these tubes is impressed upon the grids of 'triodes 450 and 45| respectively through blocking capacitors C452 and C453 respectively.

The screen potential is adjusted to a value such that the -60 volt grid bias corresponds to zero plate current as indicated by complete silence in the speaker. This adjustment may be readily made with no pedals depressed and the piano damper pedal released. R448 is made adjustable to accommodate tubes of slightly differing plate current 'cutoff characteristics.

Y The grids of the triodes 450 and 45| are connected to ground through grid resistors R454 and l R455 as well as through high frequency by-pass capacitors C456 and C451 respectively. The cathodes of the triodes 450 and 45| are connected to ground through a common self-bias resistor R458. The plates of the triodes 450 and 45| are connected to the terminals of the primary winding of a driver transformer T460, the center tap of which is connected to a suitable source of plate potential such as +350 V. terminal. The secondary of transformer T460, the center tap of which is grounded, is connected to the input of a pushpull power amplifier 462, and the latter is coupled by a transformer T464 to a pair of speakers 456 and 451.

As mentioned heretofore, the grid bias on the pentodes 440 and 44| is-made just sufficiently great, due to the connection of the grids to the -50 V. terminal, as to cut off the plate currents of these tubes. Upon depression of any of the playing keys this grid bias is changed at a predetermined rate due to the operation of the contaotor |00, which is normally in contact with segment l 02, Segment |02 is connected to a Suitable potential source such as +300 V. through a voltage divider resistor R410 and connected to ground through a volume controlling potentiometer R412. Resistors R410 and R412 form a voltage divider determining the maximum possible potential on the segment |02. The long center segment |54 is connected to a -50 V. terminal through resistors R414 and R415, the latter resistor being arranged to be shunted upon closure of a manually operable switch 416.

The +50 volt potential is carefully chosen as representing the minimum initial volume which could ever be desired in playing with the piano. Thus the sensitivity of the pedals is no greater than is actually necessary to accompany the piano and this decrease in sensitivity makes the touch characteristic pedal playing technique easier to attain. Another important reason for making the potential correspond to a minimum initial volume rather than complete silence is that it automatically aords a very desirable reduction in the dynamic range afforded by the touch responsive feature when playing at low volumes. This greatly facilitates playing at low volumes where trouble would otherwise occur in lightly depressed pedals causing signals so weak as to fall belou7 the threshold of hearing or be masked out completely by the piano tones.

The segment |06 is connected to a junction point 418 through a conductor 419 and attack resistor 480. The conductor 419 is normally connected to ground through resistor R246, and switches |22 and 25|. It will be recalled that the switch |22 is opened prior to the engagement of contactor |00 with the segment |06 as the contactor |00 swings clockwise, and that the switch 25| is operable by the piano sustaining pedal 252. A capacitor C48 |l is connected between the terminal 418 and ground.

The operation of the instrument shown in Fig. 8 is generally similar to that of the previously described embodiments. The oscillator comprising the triodes 400, 40| and associated circuit elements oscillates continuously and impresses the signal upon the distorting triodes 4H! and 4|| which operate to transmit only the high peak portions of the signal waves. The output of the triode 4|0 has its amplitude materially reduced by the capacitor C423, and the signal thus modified, together with the relatively high amplitude output signal of the triode 4||, is impressed upon the input of the phase-inverter triode 428. Since the signal pulses of the triodes 4|0 and 4| are in time phase relation, the signal impressed upon the phase-inverter triode 428 will comprise a succession of pulses in which alternate ones are of higher amplitude than the intermediate pulses, the intermediate pulses being consequently more rounded, with the result that the combined signal will be heard as the fundamental tone with its harmonics and the octave of the fundamental, likewise with its harmonics, namely, the well known octave coupler effect. This octave coupler elect will be most pronounced at the low frequency end of the pedalboard.

'I'he charge normally on the capacitor C222 due to the engagement of the contacter 200 with the segment |02 will be determined by the adjustment of the Avolume controlling variable resistor R412 to be of a relatively high value somewhere between 0 (ground) and +50 volts so that as the playing pedal or key is depressed and the contactor |00 wiped past the segment |04, this charge will be dissipated through the resistor R224, and, at one of two pre-selected rates, through the resistors R414 and R415 or through R414 alone. Thus when the contacter |00 reaches the segment |05 the charge on the capacitor C222 will depend upon the length of time that the cont-actor engaged the segment |04 and thus open the velocity at which the pedal was depressed. This charge is then applied to the capacitor C48| through R480 and the charge divided with the latter capacitor, the rate at which this transfer of charge takes place, and hence the rate of tonal attack, being dependent mainly upon the values of R480 and 048|. Since R444 is of relatively high value, in the order of 5 megohms, the potential change on the capacitor 040| will appear on the grids of the control pentodes 440 and 44| and render the latter capable of transmitting the signal. Capacitor C48| may be equal in value to C222, and resistor R444 may be equal to R224.

If the playing pedal or key is held depressed, the switch |22 will, of course, be open, and the charges on the capacitors C222 and C48| will decay at. a, rate .determinedy mainly.Y by. the values of: R224 andR which are sufficiently great to cause gradual or slowdecay. Howeven'when the playing pedalis released andthe piano sustaining pedal 252 is not. depressed the switchesl l22 and 25.1A are closed andthe charge on the capacitor CAB-I is rapidly dissipated. through the relatively low value'resistor R426 and switchesy 122. and 25| If the sustaining pedal is. depressedV and. the playing key released. the charge on the capaciter. C48! can beY dissipated only through flow. of current to the -6l1 V. terminal.thrcughRllMxand the note Will therefore decay very gradually. This is.` likewise true. if the playing key. or pedal is held depressed sulliciently tohold openthe switch` I 22. This is because the; time constant of R444 and C484- equals that of R224^ and C222. Thus the variable gain. pentodes 440 and 44| are used as volume controllingv devices and do not distort their input signals. l

The, combined instrument utilizing the electrical circuitsot Fig. 8 is played in the same manner as the previously described embodiments. it beingv possibleto produce bass tones having an. in.- tensity determined by the velocity of. pedal depression, and having a slow decay rate if the piano sustaining pedal is depressed, or the depressed. tone controlling pedal is held depressed, or having a rapid decay rate if the depressed tone controlling pedal is released While the sustaining pedallis notdepressed.

Thecombned instrument is capable of produc.- ing. many acoustic eiects. and. musical results not obtainable with the piano alone, even assuming that some. means were provided to permit operation. of the bass keys of the piano by means of a .pedal clavier. For example, the bass tone. produced' by the electrical. portion of the instrument may be damped by release of the sustaining pedal. When the instrument is played withv the piano sustaining pedal depressed', then as successive pedals of the pedal clavier are depressed each tone produced by the electrical portion of. thei'nstrument WillV continue sounding only until an.-

other pedal is depressed. This result, could not be, obtained by the piano. alone since it would require a technique almostl impossible of achieve.- ment. to. manipulate the playing keys and sus,- taining pedal in suchv a manner as to. damp. the

strings of' one note immediately prior to the, de-

'pression oi another key. Using a conventional piano,V a pianist is limited to producing either of two eiects. with reference tothe playing. ot the bassv accompaniment:- he may hold the sustaining pedal' down while depressing successivebass keys in which case the result willbe,y if the Dassage is of ordinary tempo, that. several of the bass tones will be. sounding simultaneously to pro,- duce a muddying dissonant effect; orL on the other hand,l if the player attempts to operate the piano sustaining pedal just prior to the depression of each successive. bass key, there Will be inte-rvals of silence between the successive tones. The

latter elTect is especially undesirable. in non-Itcverberative rooms, while the former eflect is undesirable under practically all conditions.

In the rendition of many musical' selections, it will be found that the left hand Will have to lexecute a low bass chord and then several higher bass chords, and in many cases this shift ofthe hand through an octave or more along the keyboard must be executed rather rapidly. Such rapid execution makes it, extremely diflcult for the player to strike the keys for lovtT bass chord with the proper velocity since the players hand must be moving rapidly, toward the low. bass chord and then. slow up suddenly to strike this chord. lightly should this be desirable in the rendition o f. theselection. This limitationis. not present in the instruments herein disclosed,since thebass accompaniment tone may be sounded. at practically any desiredintensity, depending only upon. thevelocity ot depressionr of. the basspedal,

In., the several embodiments of the invention the initial tuning of the oscillator to a predetermined frequency is accomplished. by adjustment of the variable inductances L|50 (Figs. 5 and 8), 1:1392; (Fig. 6). In, general, it4 will usually be found. desirable to,v have theV4 pitch range of, the

; oscillator beiromA 32.703 C. P. S; to 61.735' C. P. S..

These frequencies represent the frequency of the high, amplitude peaks of the output. wave 2l6 (Fig. 5). The interposition of the intermediate low amplitude peaks will result in the addition ofthe octave and its harmonicssothat the tones produced. will contain fudamental tonesof 32.7.03 to 61.735 C. P. S. plus their harmonics as Well as tones of. 65.406 C. P. S. to 123.470. C. P. S. and their harmonic partials.

The constants of the intensity envelope con.- trol circuits are preferably such thatl the intensity range of the electrical portionof the instrument is` of. thev order of r26 db.,l and thus comparable to the. dynamic ranger of the piano portion.

By the. use of any of the severalforms of the invention. the musicianv is able to render a large Variety of musical. compositions of an orchestral character with. great facility since his left hand is free to, play additional accompaniment and counter melody partsV simultaneously with the bass. part. which is played on the pedal clavier. Furthermore, music in rapid tempo. may be readily performed because the player-sv left hand need cover but a relatively narrow range. of the keyboard and'. the players foot need only cover the short compass of the bass clavier. The limitation. in playing technique, due tothe time interval which has heretofore been necessary for the pianist to move his left hand from the low bass.. register of thev piano to the middle accom.- panirnent register,` is removed.`

Because the sustaining feature of the electrical portion of the.r instrument is, controlled by the sustaining. or sostenuto pedals of the piano, or by both, vthe. player need. only tap the pedals to produce the bass tones. As explained here,- tofore, following ther tapping of one bass. pedal the players foot is. free tomoye leisurely toward the next bass pedal., Thus it becomes an easy matter for the player accurately to locate. his foot over each pedal before depressing it.

A further important musical result achieved with the apparatus of this, invention is that. of aY general' legato eiect, which is attained because, throughout most. of the time that the instrument being played, there is. some sound being pro.- duced by the bass instrument, except for the brief intervals of time during which the piano damper pedal is released. This degree of legato playing is highly desirable in rooms which are non-reverberatlve.. It. would be impossible to achieve this eifect on the ordinary organ type of pedal clavier because of. the relatively long interval. of time required to. move the foot from one pedal to another. during which time the legato effect Would be lost.

Upon depression of a pedal the oscillator is immediately tuned; to a frequency related tothe pitch of the note represented by the pedal,Y and it will continue oscillating at this frequency until adem-isa another pedal is depressed, but when a second pedal is depressed the frequency of oscillation changes instantly to that related to the second depressed pedal. Rapid passages may therefore be played on the pedals without having any overlapping of successive tones even though the Sustaining pedal is held depressed. This eiect cannot be obtained on the piano, for the piano strings continue vibrating after the key is released, and in playing rapid passages in this manner, the simultaneous sounding of a number of bass tones produces a muddy eiect. It would be impossible for the pianist to avoid this eiect by releasing the sustaining pedal just prior to depressing each key. This would require too rapid operation of the sustaining pedal and would necessarily result in discontinuities in the tonal output of the piano.

The tonal output of the combination instrument is far superior to that which could be obtained from the piano alone even if the piano were played by two musicians, one devoting his attention solely to the bass score. The instrument is relatively simple in construction and may be economically manufactured so as to be available to a large majority of owners of pianos. It may readily be combined with the piano merely by suitably arranging for the operation of the switches by the sustaining, or by either the sustaining or the sostenuto pedal of the piano. The addition of the electrical portion of the instrument to a conventional piano can therefore be accomplished without materially altering the piano structure or in any way disguring it.

While two forms of the invention have been disclosed herein, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. We therefore desire, by the following claims, to include within the scope of our invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the inventionY may be obtained by substantially the same or equivalent means.

We claim: 1. In a pedal clavier for electrical musical inlstruments, the combination of a plurality of relatively long natural pedals, a plurality of relatively short sharp pedals, pivots for said pedals,

Asaid pivots being substantially at the centers of the pedals whereby the rearward ends of the pedals will have substantially the same travel upon equal depression of their forward ends, a i pivoted bail having a rod extending across the ,movement of the bail upon the depression of a pedal to move all of the latches out of switch engaging position and to return them to switch engaging position prior to the commencement of the return strokes of the bail and pedal.

2. In a pedal clavier for electrical musical instruments, the combination of a base, a plurality of pedals pivotally mounted on the base, a rod extending across the pedals so as to be moved `upon depression of any of the pedals, a switch for each of the pedals, a switch actuator secured to each of the pedals for operating its associated 20 switch, a latch for each of the switches to hold itin operated position, and means operating by the movement of the rod during the depression of a pedal to move all of the latches out of switch engaging position and to return them to switch engaging position prior to the commencement of the return strokes of the rod and pedal.

3. In a pedal clavier for electrical musical instruments, the combination of a plurality of depressible pedals, a switch for each pedal, means carried by each pedal for operating its associated switch upon the down stroke of the pedal, latches to hold only the switches in operated position, and means to render all of the latches ineffective during a portion of the down stroke of the pedal.

4. In a pedal clavier for electrical musical in'- struments, the combination of a plurality of natural and sharp pedals, said pedals having down strokes of substantially equal length, means supporting said pedals for pivotal movement, said means being located substantially centrally of each of the pedals, a bail having Vits cross rod positioned above the rearward ends oi all of the pedals, a switch operable by each of the pedals, a latch for each of said switches to hold the latter in operated position after its pedal has been released, and means operated by the bail to move all of the latches to ineffective positions upon the depression of any pedal `during the down stroke thereof.

5. In an electrica] musical instrument, the combination of a t-one signal generating system, an output system including electroacoustic translating means, a plurality of pedals forming a pedal clavier, a plurality of switches respectively operable by the pedals, means controlled by the operation of said switches to determine the pitch of the tone signal transmitted from the generating system to the output system, means to maintain the last operated switch in operated condition until another switch is operated, a member common to all of the pedals and operated by the depression of any yone of the pedals, and a tone intensity envelope controlling means operated by said member.

6. In an electrical musical instrument, the combination of an electrical tone signal generating system, an output system including an amplifier having a terminal the potential of which determines the amplitude of the output signal, a plurality of pedals forming a pedal clavier, a plurality of switches respectively associated with said pedals and operable thereby, means controlled by the switches to determine the pitch of the tone signals transmitted from the generating system to the output system, a latch for each of said switches to hold it in operated position, a member common lto all of the pedals and operated upon the depression of any pedal, means operated by said member to render all of said latches ineffective during the down stroke oi a depressed pedal, switching means operated by said member, and a capacity and resistance network connected to said switching means and to said terminal and operable to control the potential of the terminal in response to the velocity of pedal depression.

'7. In an electrical musical instrument for use in conjunction with a piano having a sustaining pedal, a pedal clavier comprising a plurality of pedals each having a resilient means to bias it to normal position, means for producing musical tones in response to the depression of pedals of the pedal clavier, and means responsive to the depression of the piano sustaining pedal to cause 21 the tones to continue sounding after-the pedal of'V the pedal clavierl has beenreleased and re= turned tor normal posit-ion.

8. In a musicaliinstr'ument comprising an electrical output system including electroacoustic translating means, a piano' having asustaining pedal, a tone signal generating apparatus providing frequencies ofv the l'ow' bass register, a pedalv clavier, means operated by .the pedals of the clavier to cause transmissionl to the-output system of tone signals from the'generating apparatus of pitch corresponding toa depressed pedal, means tocause the generating'V apparatus to continue to supply the signalto-the outputV system at a decaying amplitudeV after the depressed pedal has been released, and means operated by the release of .the sustaining pedal of; the piano to render said last named means ineiective and thereby cause the signal amplitude to decrease rapidly' to zero.

9. In an electrical musicali instrument having an output system including: electroacoustic translating means, thev combination of an. electrical generator capable of producing musical tone signals of the pitchesof the notes of themusical scale,v a pedal clavier comprising a plurality of pedals, resilient means for each of the pedals to return. it to normal positionlwhen it is released, aA plurality of devices respectively operable by said pedals to cause musical tonesignals of corresponding pitch to be transmitted from thev generating system to the-output system, means associatedfwith each of said devices to hold itin operated position after the pedall which operated it is released and has been returned to its normal position, and means operable upon depression of anyA of the pedals to release all; of saiddevice holding means.

10. In an electrical musical instrument having an output system including electroacoustic translating means and an amplierhaving a terminal the potential of which determines the: intensity of the tonal output of the instrument, a plurality of keys forming a pedal clavier, a member moved upon depression of any one of the pedals, three contact segments, a contactor moved by said member to make contact successively with the first, second and third segments as themember is moved by the depression of a: pedal, means for maintaininga relatively high potential on the rst segment, means including a resistor connecting the second. segment to a point of` relatively low potential, means including. a resistor connecting the third segment to said terminal, a capacitor having one terminal thereof. connected to the contactor and the other terminal thereof connected to the point of relatively low potential, a relativelyy high resistance inl parallel withlsaid capaciton. andA a second capacitor connected between saidterminaland.apoint of relatively low potential, whereby when saidcontactor engages the rst segment saidiirst capacitor will receive a high potential charge, as said contactor engages said second segment the first capacitor will be dischargedat a rate determined by the rst resistor, and asth'e' contacter engages the third contact, part of theremainlngV charge on the nrst capacitor willcharge theA second capacitor andl thereby determine the potential on the; terminal.

1'1. In an electrical; musicalinstmmenthaving a plurality of. playing keys: and anf outputzsystem including a terminal. A, the potentiaL of` which determines the amplitude of! the outputy signal, a; terminal; B5 off xed relatively: potentlali. a

terminal C off ii'xed' relativelyy low potential, a terminal D of ground potential, a commutating switchcomprisng three segments and a key operated contactor successively contacting the first, second and third segments as a key is depressed, means connecting terminal-Btc the rst segment, a capacitorshunted by a highresistance connected betweenV said contacter and terminal D, a resistor connecting the second segment with terminal C, a conductor connecting the third segment with terminal A, a second capacitor oonnect'edbetween terminal A and terminal D, a circuitv including a resistance and two switches con'- necting the thirdsegment to terminal D, means operated upon depression of any of the keys to openthe iirst of said pairs of switches as thecontactor is in engagement with the second segment and to hold it open while the contacter is in engagement with the third segment, and a sustaining pedal for operating the second of the pair of switches.

l2'. In an electrical musical instrument having a plurality of playing keys and an output system including a terminal A, the potential of which determines the amplitude of the output signal', a terminal B of xed relatively high potential, a terminal C of xed relatively low potential, a terminal D or ground potential, a commutating switch comprising three segments and a key operated contacterV successively contacting the rst, secondL and third segments as a key is depressed, means connecting terminal B to the rst segment, a capacitor shunted by a high resistance connected between said contacter and terminal Dga resistor connecting the second segment with terminaly C, a conductor connecting the third segment with terminal A, a second capacitor connected between terminal Av and terminal D, a circuit including a resistance and a switch connecting the third segment to terminal D, and means operated upon depression of any of the keys to open the last named switch as the contactor is in engagement with the second segment and'to hold it open while the contacter is in engagement with the third segment.

13,. In an electrical musical instrument, the combination of an electrical tone signal generating system, an output system including an amplifier having a terminal the potential of which determines the amplitude of the output signal, a plurality of pedals forming a pedal clavier, a plurality of switches respectively associated with said pedals and operable thereby, means controlled by the switches to determine the pitch of the tone signals transmitted from the generating system to the output system, a member common to. all of the pedals and operated upon the depression of any pedal, switching means operated by said member, and a capacity and resistance network connected to said terminal and said switchesand operable to control the potential of the terminal in response to the velocity of pedal depression.

14. In an electrical musical instrument, the combination of a tone signal generating system, anoutput system including electroacoustic translating means, a plurality of pedals forming `a pedal clavier, a plurality of switches respectively operable by the pedals, means controlled by the operation of said switches to determine the pitch of the tone signal transmitted from the generating system to the output system, a member common to all of the pedals and moved. by the: depression. of any one of the pedals, and a tone intensity envelope controlling means operated by said member.

15. In an electrical musical instrument having a pulse generating oscillator operating in push pull, a pair of electron discharge devices having their input circuits connected to the oscillator in push pull, each of said devices including a cathode, control grid, and plate, a plurality of playing keys, means controlled by said keys to determine the frequency of oscillation of the oscillator, a pair of sources of plate current for said devices, each of said sources including a capacitor and a resistance network, said networks having different time constants, and means operated upon the depression of any of the keys to charge said capacitors to potentials of value determined by the velocity of key operation.

16. In an electrical musical instrument having an electrical tone signal generating means and playing keys for controlling the pitch of the output signals produced thereby, an output system including a pair of electron discharge devices having signal pulses supplied thereto in 180 phase relation by said signal generating means, a source of plate current for said devices, each including a capacitor, means to discharge said capacitors at different rates, and means for charging said capacitors to potentials determined by the velocity of operation of a key, whereby the amplitude of the signal pulses transmitted by one of said devices will decay to zero amplitude more rapidly than the signal pulses transmitted by the other of said devices.

17. In an electrical musical instrument having an output system including electroacoustic translating means, electrical means for generating electrical musical tone signal pulses in substantially 180 phase relation, a pair of control tubes for controlling the transmission to the output system of the electrical tone signal pulses, one of said tubes receiving the pulses in 180 phase relation with respect to the pulses received by the other tube, means including resistance and capacitance networks respectively associated with said control tubes to determine the amplitudes and decay rates of the output signals thereof, said networks having different time constants whereby the pulses of one phase will decay more rapidly than those of the other phase.

18. In an electrical musical instrument having an output system including electroacoustic translating means, electrical means for generating electrical musical tone signal pulses in 180 phase relation, a pair of control tubes for controlling the transmission to the output system of the electrical tone signal pulses, one of said tubes receiving the pulses in 180 phase relation with respect to the pulses received by the other tube, and means having diiferent decay rates respectively associated with said control tubes to determine the amplitudes and decay rates of the output signals thereof, whereby the pulses of one phase will decay more rapidly than those of the other phase.

19. In an electrical musical instrument having an oscillator forming a source of signal pulses in substantially 180 phase relation, a pair of electron discharge devices having their input circuits connected to the source to receive alternate pulses therefrom, each of said devices including a cathode, control grid, and plate, means biasing said devices to diiferent plate voltage cut-off potentials, a plurality of playing keys, means 'controlled by said keys to determine the frequency of oscillation of the oscillator, a capacitor forming a source of plate current for said devices', and means operated upon the depression of any of the keys to charge said capacitor to a potential of value determined by the velocity of key operation.

20. In an electrical musical instrument having a tone generating system and an output system, the combination of a plurality of pedals forming a pedal clavier, a plurality of relays each having a switch operable to determine the pitch of the tone signal transmitted to the output system by the generating system, a circuit completed upon the depression of each pedal for energizing its associated relay, a second circuit for energizing each relay, a source of electrical energy common to all of said second circuits, means operated by each pedal to disconnect said source from said second relay circuits after the first enn ergizing circuit has been completed and operable upon release of the pedal to connect said source to all of said second relay circuits and thereafter to open the first completed relay energizing circuit, whereby the relay energized upon the last depressed pedal will remain energized until another pedal is depressed.

2l. In an electrical musical instrument the combination of an oscillator, means operable to tune the oscillator to any one of the frequencies of the notes of the musical scale within the gamut of the instrument, a plurality of depressible keys for operating the tuning means, resilient means for each of the keys to return it from depressed to normal position, means to maintain the oscillator tuned at the frequency represented by the last operated key until another key is operated despite the return of the depressed key to normal position by its resilient means, and tone intensity envelope controlling means having its operation initiated by the operation of any one of the playing keys.

22. In an electrical musical instrument having an output system including electroacoustic translating means, a plurality of playing keys, ap-

paratus controlled by the keys for generating tone signal pulses having-a push-pull output, a pair of electron discharge devices each having a cathode, control grid and plate, means for impressing the signal pulses produced by said generating apparatus upon the grids of said devices in push pull, means including a charged capacitor and controlled by the keys for supplying plate current to said devices, and means connecting the cathodes of said devices to points of diierent fixed potentials, whereby, as the capacitor discharges through the plate circuits of said devices, one of the Vdevices will attain zero signal transmission before the other.

23. In an electrical musical instrument having playing keys, the combination of a source of audio frequency signals having wave shapes of generally symmetrical rectangular character, an electron discharge device having a cathode, control grid and plate, a circuit for impressing signals from said source upon the control grid, means for altering said Wave shape including a current limiting capacitor-resistance mesh connected to the control grid of the electron discharge device, means providing a constant relatively large fixed negative grid bias on the device, thereby to provduce asymmetrical plate current pulses of time shorter than the period of the rectangular input pulses, and means for applying to the plate of vsaid device a variable potential whose value is Viepenclect upon the velocity with which a playing assunse 25 key l'is depressed, thereby to produce Aan output .signal of "corresponding amplitude.

24. In an electrical musical I'instrument 'having playingkeysjthe'combination of a source of audio 'frequency signals having Wave 'shapes Aoi Ygener- 'a'llysymme'trical character; an electron-discharge device having 'a'cathoda `control grid, and plate; a circuit for impressing signals from said source upon thecontrol grid; means 'for altering fthe si gnal-wave shape to provide asymmetrical plate-curfrentipulses `o1 shorter `duration than those pro-- vided 'by the source, said last `named vmeans comprising a :current limiting .capacitor-resistance lmesh'connecteclto the grid, and means providing a 'constant relatively large grid bias on the fdc-- vice; fasecond electron discharge-device coupled in series with said Vnrst device; `and means to 'apply to the plates of bothoi 'said Adevicesva'vari- Iable potential, the of which vis :dependent upon `the velocity with which a playing key is depressed, thereby to produce van output -signal :o'f vcorresponding amplitude and to cause complete cessationiof signal transmission i-.by the sec `ond device When the pa'te potential applied 'to both of said devices is zero.

25. :Inan 'electrical musical instrument having an-output System and-a clavier comprising a plu- :ralityoi keys, an oscillator capable of being tuned vthroughout ya range of frequencies corresponding fto that ofthe clavier, meansroperable by each of the :keys to tune the oscillator to a lfrequency srelated to that of A`the operated key, resilient means toreturn each of the keys to normal position without affecting the position of one ofthe named means which may'fhave'beenoperated, means'f'or causing 'the oscillator to continue os- 'cillatingiat the Vfrequency of the -last operated key Auntil the operation of another 'key which rrequires that the oscillator be tuned to a different `frequency, additional switch means operated -by the fdepress'ionfof any one of the keys,=and signal intensity controlling means forming 'part-of the out- :put system and rendered eilective by the additional'switch means.

26. An electrical 'musical instrument comprisimg, a plurality of depressible resilientlyreturned keys, a variable frequency oscillator, means lo perable by the'keys totune the oscillator-.toa frequency'which is related to the Ypitch of the 'depressed key, a -latch mechanism for 'holding 'the v'tuning lmeans 1in operated position despite the vrelease and returnof the 'key which operated the tuning means, .and 'means for causing the oscillator to operate at thefrequency .to which it has "been tuned until a key calling for v'an unrelated pitch is depressed.

27. The combination -set forth in claim '26 'in 'which Vmeans are provided to .cause the signal provided by .the oscillator 'to decay at -a ,predejtermined rate.

'28. 'In an electrical musical .instrument having an output system and .a keyboard .comprising a .plurality of keys, La -musical .tone .signal generat- Wing `system for supplying to the output system lsignals of pitches related respectively to nthekeya .-meansoperablerby `.the keys tocause the generat- :ing :system to transmit to .the output :system :an -felectricalsignal of a pitch relatedrto 'a depressed key and to continuetransmitting the signal 'tothe r :output system until .the depression of another 'key which requires that a tone signal of different pitch *be supplied tothe output system, and tone intensity envelope vcontrolling means -in the `outmut system loperable 'to lclock transmission of the 2.6 signal through the output system a predetermined time iinterval after v'the release of a key.

29. A musical instrument comprising a vpiano having a sustaining pedal, and a pedal `clavier associated with the piano for simultaneous playing therewith, said-pedal claviercomprising a plurality vor pedals; an electron discharge tube oscillator; means operated fby the pedals for tuning the'osclllator'to pitches related respectively to the pitches lrepresented 'by `the pedals; means to cause said last named -:means associated with one pedal to remain effective until the corresponding means :associated with another pedal is operated; means operative upon the signal supplied by the oscillator to'cause it todecay at a predetermined rate when the piano sustaining pedal is depressed; -and means operated upon release of the piano 4sustaining-pedaltocause the signal to decay at a 'different rate.

3G. 'In an electrical musical instrument, the 4combination of a variable frequency oscillator having a tuning circuit including a plurality of tuning elements, a plurality of playing keys, resilient means to return operated keys to normal position, switches respectively operable by the keys and zconnected -in the tuning circuit, each of the Vswitches 'being eiective `upon operation of its associated key to cause the connection in the tuning Jcircuit vof predetermined tuning elements, 1la'tching means to maintain the Aswitch in operated position luntil a key requiring the tuning of the oscillator to a vdifferent frequency is depressed, said latching means permitting returning voi' YVthe keys to normal position, and means to maintain the other switches in a position to prevent lthem 'from vchanging the tuning of the oscillator from lthe frequency to which it was -tuned 'bythe 'operation of the last depressed key.

31. AIn an electrical musical instrument, the combination of a variable frequency oscillator having Aa tuning circuit, a plurality of playing 'keys, `Aresilient means to return depressed 'keys to normal position, means operated by the playing keys to tune the oscillator to a predetermined `frequency related to that represented by an operatedikey, and means to maintain the oscillator tuned to such frequency, despite release of the key and its return to normal position, until a diiferentlkey requiring the oscillator to be'tuned "to'adiierent frequency is operated.

'32. In an velectrical musical instrument, the Acombination vof a variable frequency oscillator, a plurality of )playing keys, resilient means to Irev5turn operated keys to normal position, means loperable ley-each of said keys to tune the oscil- 'lator -to a frequency related `to that represented by an operated key, and means to maintain the oscillator tuned tothe frequency of the operated '-key -until "a second key is operated calling for the tuning -of the oscillator toa different frequency, despite the previous release'and return to normal position Vof the `ilrst operated key.

v33. In Aan electrical musical instrument, electrical musical tone signal generating means `supplying two 4harmonically complex pulse type wave 4form signals Vvof the same fundamental Vfrequency bu'tof opposite phase, two separate Atransmission -channels fcoupled to the generating means for :transmitting respectively the two signals, means 'for-combiningthe output signals of the'two chan- `nels and ytranslating the combined signal into sound, and reactive means associated with oneof thefchannels eiective to'increasethe disparity of the amplitudes of the two signals transmitted respectively by the two channels 'as the vfrequency 27 ofthe signals is increased, whereby a. reduction in the octave coupler tonality effect is obtained as the frequency of the signalsis increased.

34. In an electrical musical instrument having an output system which includes a terminal the potential of which determines its gain, a pedal clavier comprising a plurality of pedals each operating five switches, namely, a first, a second, a third, a fourth, and a fifth switch, each pedal upon depression being arranged rst to open the first switch and close the fifth switch and thereafter to open the second and fourth switches and close the third switch, a potential storingcapacitor, an intensity envelope control relay having a pair of switches, a circuit including all of the third switches in parallel for energizing said relay, means connecting all of said iirst switches in series, a source of potential for charging said capacitor normally connected thereto through a circuit including said series of first switches and one of the relay switches, a relatively low impedance in said charging circuit, means connecting the second switches in series, said series of second switches being connected to said capacitor through said relay switch and being connected to a relatively low potential source through a relatively high impedance, a plurality of pitch determining relays, -means operated by each of the fifth switches to energize a pitch determining relay, individual holding circuits for said pitch determining relays, a common source of electrical energy for said holding circuits, said source being connected to said holding circuits through all of said fourth switches, means voperated by each of said pitch determining relays for causing amusical tone signal of pitch corresponding to the depressed pedal to be transmitted to the output system, and a circuit for impressing the potential of said capacitor on said terminal of the output system- 35. In an electrical musical instrument for use in conjunction with a piano having a sustaining pedal, the combination of a pedal clavier comprising a plurality of pedals, resilient means associated with each of the pedals to return it to normal position after it has been depressed and released, stop means limiting the return movement of the pedals by the resilient means, a musical tone signal generatingl system, an output system, switch means respectively operated by the pedals .to cause transmission from the generating system to the output system of an electrical musical tone signal of frequency corresponding to that of the depressed pedal, means including switches and forming part of the output system for determining the intensity envelopes of the signals transmitted through the output system, means for operating one of said switches upon the maintained depression of any one of the pedals to cause the tone signal to be sustained, and means for operating another of said switches upon the depression of the piano sustaining pedal, the operation of the last named switch also causing the tone signal to be sustained.

36. In an electrical musical instrument for use in conjunction with a piano having a sustaining pedal, a pedal clavier comprisinga plurality of depressible pedal keys each having means to return it to normal position, a bass tone generating system of complex quality, an output system including an electroacoustic transducer, elements operated by said keys for determining the frequency of said generating system during the interval of time that the key is depressed and also effective to determine the frequency of said generator after the key is completely released, an envelope determining decay apparatus associated with said generator to cause relatively rapid attenuation of the tone supplied to said transducer upon release of the pedal, and an auxiliary connection to the piano sustaining pedal to render said decay apparatus ineffective despite complete release of said keys.

37. In an electrical musical instrument for use in conjunction with a piano having a sustaining pedal, the combination of a plurality of pedal keys, a bass tone generating system of complex quality, an output system including an electroacoustic transducer, envelope determining means operable by said keys to cause the tone signals applied to said transducer to decay at a relatively rapid rate upon complete release of said keys, and an auxiliary sustaining control responsive to the depression of the piano sustaining pedal to render said envelope means ineffective despite complete release of the pedal keys.

38. In an electrical musical instrument having an electrical output system including an electroacoustic transducer, the combination of a plurality of depressible Vpedals constituting a pedal clavier, a bass tone generating system capable of producing electrical musical tone signals, switches operated by the pedals to determine the pitch of the tone signals supplied by the generating system to the output system, means to hold the switches operated by the pedals in operated condition, a member common to all the pedals and operable by any one of the pedals to render all of the switch holding means temporarily ineffective during the depression of any pedal, control means associated with the output system normally rendering it incapable of transmitting to the transducer the tone signals supplied by the generating system, means affected by the depression of any pedal to cause the control means to transmit the tone signals while the pedal is depressed, and a sustaining switch operable at will by the player and connected to the control means to cause the latter to continue to transmit the tone signals after the pedal has been released.

39. An electrical bass tone producing instrument for use in the accompaniment of a piano which has a sustaining pedal, comprising, an output system including an electroacoustic transducer, a pedal clavier including a plurality of pedals, depressible from normal positions, a bass tone signal generating system to generate and transmit to the output system electrical tone signals, means operated by the vclavier pedals to determine the pitch of the tone signals transmitted to the output system by the generating system, means to cause decay of the tone signals to inaudibility upon release of the clavier pedals and their return to their normal positions, and a connection between the piano sustaining pedal and the last named means to render the latter ineffective while the sustaining pedal is held depressed despite the release of the clavier pedals.

40. In an electrical musical instrument to be played in conjunction with a conventional piano having a sustaining pedal, the combination of the pedal clavier comprising a plurality of pedals, an electric output system, a tone signal generating system, means controlled by staccato depressions and release of the clavier pedals to cause the generating systemto transmit to the output system tone signals of a frequency corresponding to that represented by the operated pedal when it is depressed and after it is released, means operable upon release of any of the clavier pedals to cause the tones to decay at a rapid rate, and means connected to the piano sustaining pedal for operation thereby to render said decay causing means inn effective.

41. In an electrical musical instrument having means for producing musical tones of diierent pitch, a plurality of playing keys, elements operated respectively by depression of said keys, the operated element determining the pitch of the tone produced by the instrument, retaining means associated With each of the elements to maintain it in operated condition upon release of its key, means operated upon the depression of any key to cause the retaining means of all other keys to release their associated elements, and means to cause the intensity of the tone produced by the instrument to decay gradually upon release of a depressed key.

42. In an electrical musical instrument to be played in conjunction with a conventional piano having a sustaining pedal, the combination of a pedal clavier comprising a plurality of pedals, an electric output system, a tone signal generating system, means controlled by the pedals to cause the generating system to transmit to the output system tone signals of a frequency corresponding to that represented by the depressed pedal While the pedal is depressed and after it has been released, means operable by any of the pedals to determine the initial intensity of the tones produced, means to cause the tones to decay at a rapid rate after complete release of the depressed pedal, and means operated by the piano sustaining pedal to render said, decay causing means inffetiv: s

43. In an electrical musical instrument for playing in conjunction with the playing of a piano having a sustaining pedal, musical tone signal producing means, a pedal clavier comprising a plurality of pedals operating on the tone producing means to select the pitch of the tone to be produced, means responsive to the velocity of the depression of any of the pedals to control the initial intensity of the tone, clavier pedal controlled means causing rapid decay of the tone, means rendering said rapid decay causing means inffective While any pedal of the pedal clavier is held depressed, and means operated by the sustaining pedal for rendering said rapid decay causing means ineiTective While the piano sustaining pedal is held depressed despite the release of the depressed pedal.

LAURENS HAMMOND. JOHN M. HANERT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,105,629 Dixon Aug. 4, 1914 1,893,895 Hammond Jan. 10, 1933 2,126,464 Hammond Aug. 9, 1938 2,126,682 Hammond Aug. 9, 1938 2,148,478 Kock Feb. 28, 1939 2,154,778 Schnell Apr. 18, 1939 2,301,871 Hanert Nov. 10, 1942 2,357,191 Hanert Aug. 29, 1944 

